Azomethine dye solutions

ABSTRACT

A process for making yellow, basic azomethine dyes for paper, leather and textiles, and concentrated, stable solutions thereof; the process being an improvement in the process of reacting an azo dye base precursor of the formula ##SPC1## 
     Wherein A is phenyl or substituted phenyl, with dimethyl sulfate in solution, and in the presence of an acid-binding agent, 
     THE IMPROVEMENT COMPRISING EMPLOYING AN AQUEOUS SOLUTION HAVING AT LEAST 30 WEIGHT PERCENT WATER, EMPLOYING DIMETHYL SULFATE IN A MOLAR EXCESS OF FROM 100% TO 300%, AND EMPLOYING FROM 2.0 TO 3.5 MOLES OF MAGNESIUM OXIDE AS THE ACID-BINDING AGENT PER MOLE OF PRECURSOR.

BACKGROUND OF THE INVENTION

The stable, concentrated, basic dye solutions of this invention areunknown in the art.

Basic azomethine dyes are used extensively in the form of relativelydilute aqueous solutions in the paper, textile and leather industries.Heretofore, dyeing solutions have been prepared by the dyer from finelyground dyes. The finely ground dyes have the disadvantage of cakingthrough the action of moisture or heat, with subsequent difficulty indissolving the dyes. Moreover, weighing or transferring the powdereddyes is attended by unpleasant dust formation. In addition, duringdissolution of the dyes and subsequent stirring, frothing often takesplace leading to consequent contamination and loss.

Use of the stable, concentrated dye solutions of this invention willinsure a more uniform dye bath strength. Also, the highly concentratedsolution can be fed into the dye bath by a simple metering process.

The novel process has several advantages over prior art processes. Thenovel process leads to pure dyes that are substantially free ofunreacted azo dye base and/or protonated dye salt contamination caused,inter alia, by not using acid-binding agents or by not using them insufficient amount. Because of this freedom from azo dye base andprotonated dye salt contamination, the dyes produce brighter dyeingshaving very good light fastness and sublimation fastness compared todyeings made with contaminated dyes.

Further, the novel process leads to dyes substantially free of thewater-insoluble carbinol form of the dye which requires an additionalacid neutralization step to be converted to the desired quaternizedform. The carbinol form sometimes results from alkaline neutralizationof the quaternized dye salt during quaternization when an alkalineacid-binding agent is employed. Detectable amounts of the carbinol formin the final dye will of course, cut down correspondingly on dyestrength and adversely affect the shade. A lowering of yield will alsooccur.

SUMMARY OF THE INVENTION

This invention concerns

1. dye solutions,

2. a process for making intermediate dye solutions, and

3. a process for making the dye solutions of 1. from the intermediatedye solutions made by the process of (2).

This invention concerns a stable, yellow, basic azomethine dye solutioncomprising

5% to 50% by weight of dye,

10% to 95% by weight of solvent,

up to 40% by weight of water, the dye having the formula ##STR1##wherein A is phenyl or phenyl substituted by 1 to 3 groups selected fromC₁₋₄ alkyl and C₁₋₄ alkoxy, and X⁻ is an anion. Preferably, thesubstituted-phenyl-containing dyes will contain one substituent group.

The novel process for making intermediate solutions of dyes of theformula ##STR2## is an improvement in the process of reacting an azo dyebase (precursor) of the formula ##STR3## wherein A is phenyl or phenylsubstituted by 1 to 3 groups selected from C₁₋₄ alkyl and C₁₋₄ alkoxy,and X⁻ is an anion, with dimethyl sulfate in solution, and in thepresence of an acid-binding agent, the improvement comprising reacting

i. dimethyl sulfate in a molar excess of from 100% to 300% per mole ofdye base,

ii. in an aqueous solution having at least 30 weight percent water, and

iii. from 2.0 to 3.5 moles of magnesium oxide acid-binding agent permole of dye base.

The azo reactant is referred to as the "azo dye base" for convenienceand simplicity. It should be understood, however, that the correspondingacid salts are also operable as reactants (precursors) and are thereforeincluded within the scope of the invention without being referred torepeatedly.

Reaction temperatures are generally maintained at between about 70°C. to120°C. Following the reaction to produce the dye intermediate, the dyecan be isolated therefrom in dry form. Isolation of the dry dyestuff canbe conducted readily at a pH below about 2.5.

An alternative to the isolation of the dry dye is to vary theconstituency of the dye intermediate that is prepared by the novelprocess outlined above, to produce the novel dye solutions of thisinvention. That is, to produce the dye solutions of this invention, anadditional step is needed to convert the intermediate dye solutions tothe dye solutions that are within the invention.

The additional process step concerns adjusting the intermediate dyesolution constituency to remove organic reaction solvent and/or water,and to add the other necessary ingredients in the requisite amounts toproduce the novel dye solutions. For the sake of simplicity the term"adjusting constituency" will be employed to encompass this process stepof adding and removing ingredients. It should be understood that such"adjusting " is conducted at a pH below about 2.5 and the term includesacidification to achieve such pH.

The anion X⁻ can be derived from an inorganic or organic acid, e.g. fromhydrohalic acids (Cl⁻, Br⁻, I⁻), sulfuric acid (SO₄ =) methylsulfuricacid (CH₃ SO₄ ⁻); from alkyl or aryl sulfonic acids (alkyl or aryl SO₃⁻); or from C₁₋₄ aliphatic carboxylic acids such as formic acid, aceticacid or propionic acid (C₁₋₃ alkyl CO₂ ⁻). Double salts of the dye saltsobtained according to the invention can often be advantageouslyproduced, especially the zinc chloride double salts. In this case, X⁻represents such complex anions as the trichlorozincate ion (ZnCl₃ ⁻).

Especially preferred solution compositions of this invention comprisebetween about 20% to 40% dye, 30% to 60% solvent, and 20% to 30% water,based on the total solution weight.

DETAILS OF THE INVENTION

The novel process is typically carried out by heating the reactionmedium comprising the azo dye base precursor to 70° to 120°C. preferably90° to 100°C., with 2.0 to 3.5 moles, preferably 2.5 to 3 moles ofmagnesium oxide per mole of azo dye base precursor in 1.5 to 5,preferably 1.5 to 2.5 parts by weight (per part by weight of azo dyebase precursor) of aqueous or aqueous-organic solvent.

Then, while maintaining the reaction temperature at 90° to 100°C., anaddition is made dropwise, in the course of 0.5 to 2 hours, of 100% to300%, preferably 140% to 200%, of the theoretically required amount ofdimethyl sulfate. Heating is continued for an additional 0.5 to 2 hours.To the reaction mixture are then added 10% to 100%, by weight of thereaction mixture, of water and sufficient acid which can be a hydrohalicacid or sulfuric acid, to bring the pH of the reaction below 2.5.Preferably, sulfuric acid is used and a pH of 1.5 to 2.0 is obtained.

The reaction medium can consist wholly of water but can also be aheterogeneous mixture of water and an aromatic, optionally halogenated,hydrocarbon solvent. Water can be used as the sole reaction medium whenthe starting azo dye base has a melting point of about 100°C. or less.Azo dye bases having melting points substantially higher than 100°C.require the addition of the aromatic cosolvents. It should beappreciated that such aromatic cosolvents are removed whether byisolation of the dry dye therefrom, or, by separation from the reactionmedium in the "adjusting" process step to achieve the novel dyesolutions. Such aromatic (reaction) cosolvents are not the cosolventsemployed in the novel dye solutions.

Useful aromatic solvents include benzene, toluene, xylene,o-dichlorobenzene, monochlorobenzene and the like. Monochlorobenzene isparticularly preferred. Aqueous-organic solvent mixtures containing from30% to 100% water and up to 70% aromatic solvent by weight are operablein the process. Incomplete solution of the starting azo dye base in theaqueous organic reaction medium generally reduces the rate ofquaternization and is to be avoided. A reaction medium consisting of 90%water and 10% monochlorobenzene by weight has provided especiallysatisfactory results when employed in the process.

After acidification of the reaction medium to a pH below 2.5, anyorganic solvent present can be removed by steam distillation. Thereupon,the quaternized basic dye separates as a concentrated oily layer whichcan be removed readily from the aqueous reaction mixture. The dyeconcentrate can then be diluted to a standard strength with suitablesolvents such as water-soluble carboxylic acids and/or otherhydroxyl-containing cosolvents and packaged in suitable containers forshipping.

An acid-binding agent must be present to obtain optimum conversion ofthe azo dye base to the quaternized dye. A comparison of such agents,e.g. sodium hydroxide, lithium hydroxide, sodium borate and the like,showed them to give 10 to 20 percent unreacted azo dye base at the endof the quaternization cycle. With magnesium oxide as the acid-bindingagent, the amount of unreacted azo dye base was reduced to a level ofone percent or less.

Using the process of this invention, it is possible to performquaternization in a more complete manner than previously and atconsiderably less expense than realized when operating in the hithertousual organic reaction media.

Examples of carboxylic acids useful as solvents in the concentrated dyesolutions of the invention are monocarboxylic acids, particularlyaliphatic monocarboxylic acids. It is required to use low molecularweight liquid carboxylic acids having six carbon atoms or less.Water-soluble hydroxycarboxylic acids are also suitable. Examples ofsuitable acids are formic acid, acetic acid, propionic acid andespecially glycolic acid.

The carboxylic acid solvents can be used either by themselves or inadmixture with one or more hydroxylic (hydroxyl-containing) solvents,for example, alcohols, glycols and glycol ethers. Suitable alcohols,glycols and glycol ethers are benzyl alcohol, diacetone alcohol,ethylene glycol, diethylene glycol, propylene glycol and ethylene glycolmonomethyl or monoethyl ether. Such hydroxylic solvents are sometimesemployed in the absence of carboxylic acid cosolvents.

A basic dye solution of the present invention can also be prepared bymixing the solid form of the isolated basic azomethine dyes with thedisclosed solution components in any order and stirring the mixture withheating if necessary. The resulting solution can be filtered to removeinsoluble residue and the concentration of the solution is adjusted byadding basic dye, water, or organic solvent as desired.

Despite the fact that the dye solutions of this invention are highlyconcentrated, they remain liquid at temperatures below the freezingpoint (e.g. -10°C.) and the dissolved dye does not crystallize out.There is, furthermore, no falling off of the concentration uponprolonged storage of the solution. The subject process provides a simplemethod of obtaining highly concentrated solutions of basic azomethinedyes which can be used directly as stable liquid commercial preparationsof the respective dyestuffs.

The basic dye solutions prepared according to this invention can be usedfor the dyeing by conventional procedures. Dyeing can also be effectedby absorption of entrained dye solution during the actual spinning anddrawing operations pursuant to fiber manufacture.

By proper selection of the anion in the subject quaternization process,the dye solutions can be prepared as chloride-free products in order toavoid corrosion of stainless steel equipment used in the trade for themanufacture and dyeing of textile fibers. The sulfate salts of the dyesare particularly useful in this regard.

The following Examples serve to illustrate the invention. All parts aregiven by weight.

EXAMPLE 1

A mixture of 175 parts of water, 33 parts of monochlorobenzene, 84.8parts (0.29 mole) of an azo dye base having the formula ##STR4## and 40parts (1 mole, 3.4 moles per mole of azo dye base) of magnesium oxidewas heated to 90° to 95°C. Dimethyl sulfate (88.2 parts, 0.70 mole, 140%molar excess) was then added over 30 to 40 minutes, while maintainingthe temperature at 90° to 95°C. The reaction mixture was then maintainedat 90° to 95°C. for an additional 30 minutes. Thin layer chromatographyon Silica Gel G plates using methyl ethyl ketone/water (10/1) as eluentindicated that over 99% of the azo dye base had been quaternized. Water(47 parts) and 142 parts of concentrated (37%) hydrochloric acid werethen added while maintaining the temperature at 90° to 95°C. The pHdropped to 1.5 to 2.0 during the acid addition. The heterogeneousmonochlorobenzene-water mixture was then cooled with stirring over a4-hour period to 5° to 10°C. The product, an azomethine dye having theformula ##STR5## crystallized out as fine yellow crystals and wassubsequently isolated by filtration, washed with 300 parts of 10% sodiumchloride solution and dried at 85° to 90°C. under vacuum. The dye waschromatographically pure. Yield: 134 parts (98%), calculated from theweight of product and its tinctorial strength as compared with apurified standard.

EXAMPLE 2

A mixture of 80 parts of water, 20 parts (0.50 mole, 2.8 moles per moleof azo dye base) of magnesium oxide and 50 parts (0.18 mole) of an azodye base of the formula ##STR6## was heated to 95° to 100°C. Dimethylsulfate (54 parts, 0.43 mole, 140% molar excess) was gradually added atsuch a rate so as to maintain the temperature in the range of 95° to100°C. The pH of the mixture was initially 9 but dropped to 6.5 uponcompletion of the dimethyl sulfate addition. The reaction mixture washeated an additional 30 minutes at 95° to 100°C. Thin layerchromatography indicated that over 99% of the azo dye base had beenquaternized. The reaction mixture was then cooled to 50° to 60°C. and asolution of 41 parts of concentrated sulfuric acid in 140 parts of waterwas added. After the acid addition was complete, the pH was 1.5-2.0. Thereaction mixture was allowed to stand while the temperature wasmaintained at 50° to 60°C. The lower aqueous layer was removed anddiscarded. The concentrated upper layer containing product of theformula ##STR7## was diluted with 200 parts of 70% aqueous glycolic acidto give a final dye solution containing 22% by weight of basic dye asthe acid-sulfate salt, 47% by weight of glycolic acid (100%) and 31% byweight of water.

EXAMPLE 3

The procedure of Example 2 was repeated except that the 200 parts of 70%aqueous glycolic acid were replaced by a mixture of 80 parts of ethyleneglycol, 80 parts of diacetone alcohol and 40 parts of water to give afinal dye solution containing 22% by weight of basic dye as theacid-sulfate salt, 27% by weight of ethylene glycol, 27% by weight ofdiacetone alcohol and 24% by weight of water.

EXAMPLE 4

The procedure of Example 2 was repeated except that the 200 parts of 70%aqueous glycolic acid were replaced by a mixture of 36 parts of glacialacetic acid and 36 parts of 70% aqueous glycolic acid to give a finaldye solution containing 41% by weight of basic dye as the acid-sulfatesalt, 21% by weight of acetic acid, 14% by weight of glycolic acid(100%) and 24% by weight of water.

EXAMPLE 5

A mixture of 180 parts of water, 75 parts of monochlorobenzene, 24 parts(0.63 mole, 2.5 moles per mole of azo dye base) of magnesium oxide and77 parts (0.25 mole) of an azo dye base of the formula ##STR8## washeated to 90° to 95°C. Dimethyl sulfate (94.5 parts, 0.75 mole, 200%molar excess) was added gradually over about a 30 minute period. Thereaction mixture was then heated for 30 minutes at 90° to 95°C. Based onthin layer chromatography, the quaternization was greater than 99%complete. Water (400 parts) was added and the excess magnesium oxide wasneutralized by the gradual addition of 61 parts of concentrated sulfuricacid. The pH of the final mixture was 1.5-2.0. The monochlorobenzene wasthen removed by steam distillation. The reaction mixture was thenallowed to stand while maintaining the temperature at 65° to 75°C. Thedye layer separated as an oil phase which was separated from the aqueousphase. The resultant hot (65° to 75°C.), concentrated oil phase,consisting of about 80% pure dye was diluted with 200 parts of 70%aqueous glycolic acid solution and 75 parts of glacial acetic acid togive a final dye solution containing approximately 24% by weight of dyeas the acid sulfate salt, 36% by weight of glycolic acid (100%), 19% byweight of acetic acid and 21% by weight of water.

Instead of a solution product, the dye can be readily obtained as acrystalline solid by omitting the aforementioned dye-oil separation stepand merely cooling to 5° to 10°C. The dye readily crystallizes and canthen be isolated by filtration and dried.

Alternately, the removal of monochlorobenzene by steam distillation maybe omitted and the heterogeneous reaction mixture cooled to 5° to 10°C.to obtain the dye as the crystalline sulfate salt. Under theseconditions, the filter cake is washed with a 10% solution of aqueoussodium sulfate to aid in the removal of some of the monochlorobenzenefrom the filter cake before drying.

A solution product of the dye may also be obtained by using the isolateddye sulfate salt and 70% glycolic acid alone or a mixture of glycolicacid and acetic acid as the solvent to provide dye solutions containingfrom 20% to 30% dye by weight.

If the presence of chloride ions is not objectionable, the dye can alsobe isolated as the chloride salt by neutralizing the reaction mass with106 parts of 37% aqueous hydrochloric acid instead of with sulfuricacid. Again by cooling to 5° to 10°C., with or without steamdistillation of the monochlorobenzene, the dye crystallizes mainly asthe chloride salt and can be isolated by filtration and dried.

EXAMPLE 6

The procedure of Example 5 was repeated except that the 200 parts of 70%aqueous glycolic acid and 75 parts of glacial acetic acid were replacedby 275 parts of 70% aqueous glycolic acid to give a final dye solutioncontaining 24% by weight of basic dye as the acid-sulfate salt, 49% byweight of glycolic acid (100%) and 27% by weight of water.

EXAMPLE 7

A mixture of 200 parts of water, 75 parts of monochlorobenzene, 24 parts(0.63 mole, 2.5 moles per mole of azo dye base) of magnesium oxide and80 parts (0.25 mole) of an azo dye base of the formula ##STR9## washeated to 90° to 95°C. Dimethyl sulfate (94.5 parts, 0.75 mole, 200%molar excess) was added gradually over a 30 minute period. The reactionmixture was heated an additional 15 minutes at 90° to 95°C. Based onthin layer chromatography, the quaternization appeared to be essentiallycomplete. Water (400 parts) was added and the excess magnesium oxide wasneutralized by the addition of 61 parts of concentrated sulfuric acid.The pH of the mixture was 2.0. The reaction mixture was cooled to 10° to15°C. in order to precipitate the dye, which was subsequently isolatedby filtration, washed with 10% aqueous sodium sulfate solution to removesome of the monochlorobenzene and finally dried to give 110 parts ofpure basic dye as the acid-sulfate salt.

A concentrated solution product of the dye was obtained by dissolvingthe isolated dye salt (26 parts) in 30 parts of glacial acetic acid and44 parts of 70% aqueous glycolic acid to give a final dye solutioncontaining 26% by weight of basic dye as the acid-sulfate salt, 30% byweight of acetic acid, 31% by weight of glycolic acid (100%) and 13% byweight of water.

The embodiments of the invention in which our exclusive property or privilege is claimed are defined as follows:
 1. A stable, yellow, basic azomethine dye solution comprising5% to 50% by weight of dye, 10% to 95% by weight of at least one member selected from the group consisting of carboxylic acids of one to six carbon atoms, and water-soluble hydroxycarboxylic acids, and 0 to 40% by weight of water, the dye having the formula ##SPC2##wherein A is phenyl or phenyl substituted by 1 to 3 groups selected from C₁₋₄ alkyl and C₁₋₄ alkoxy.
 2. A solution according to claim 1 comprising20% to 40% by weight of dye, 30% to 60% by weight of solvent, and 20% to 30% by weight of water.
 3. A solution according to claim 1 wherein A is phenyl.
 4. A solution according to claim 1 where A is p-methoxyphenyl.
 5. A solution according to claim 1 wherein A is p-ethoxyphenyl.
 6. A solution according to claim 2 wherein A is phenyl.
 7. A solution according to claim 2 wherein A is p-methoxyphenyl.
 8. A solution according to claim 2 wherein A is p-ethoxyphenyl. 